Provides traffic cost estimation of a transaction submission (confirmation request + response) Current assumptions and known limitations: Exact addressing of confirmation request and response depends on whether the executing participant hosts the relevant parties. To simplify, the logic assumes that this node will be the executing participant. This also has an impact on the number of session encryption keys. External signatures number and type impact the final payload size and therefore cost. Hints can be provided to improve accuracy. In the absence of hints, the estimation uses the threshold-first keys registered in the external party's PartyToKeyMapping